Some justices see the law as a slippery slope, but we have been on such slopes before and the court has easily been able to limit federal power.

Twenty-six attorney generals, who are the plaintiffs of the lawsuit against… (Alex Wong/Getty Images )

The Affordable Care Act faced a possibly fatal challenge last week when the constitutionality of its individual mandate provision was argued in the Supreme Court.

Much of the terrain was easy going. Neither the justices nor the lawyers doubted that the healthcare and healthcare insurance markets involve interstate commerce — insurance and healthcare providers are usually national or at least regional operations, folks who cross state lines get sick and must be cared for away from home regularly, and people are often unable to relocate to another state for fear of losing employer-based coverage. Nor was it disputed that the mandate was sincerely motivated by and closely related to the regulation of these interstate markets. Those two conclusions are usually sufficient to justify the exercise of congressional power under the commerce clause of the Constitution.

But then things got more treacherous. The problem, suggested by numerous questions from the conservative justices on the court, was the slippery slope they saw created by the mandate — the idea that Congress was requiring individuals to buy something. If the feds can require each person to buy health insurance, what can't they force people to purchase?

Some justices worried: Would Congress also be able to force people to buy cellphones, or broccoli, or burial services? Once you start allowing Congress to compel people to purchase goods or services, aren't you in a free fall that has only one conceivable end point — a world with no limits to the federal government's commerce-clause power to regulate the lives of all Americans?

Strangely missing from these exchanges was any recognition that we are already poised on equally treacherous slopes in interpreting the commerce clause, and the court has demonstrated that it has plenty of pitons available to it to arrest our slide and limit the scope of federal power.

To understand this, remember that the court has already determined Congress has authority to prohibit people from possessing things under the commerce clause. Just seven years ago in Gonzales vs. Raich, the court held that the feds can ban the possession of marijuana. It didn't matter how a person obtained the marijuana, how much he or she possessed or whether he or she planned to consume rather than sell it. Possession itself could be prohibited.

Talk about slippery slopes! Does the Raich case mean Congress can also ban possession of cars, televisions, clothes, the gingerbread cookies that Grandma baked and brought over last week, the tomatoes you grew in your garden or the broccoli in the refrigerator? What can't the federal government do, if it can ban the possession of goods?

Don't panic. The government's power to ban possession of things is not unlimited. As Justice Antonin Scalia observed in his concurring opinion in Raich, the possession of marijuana in particular can be punished because such penalties are necessary to carry out a comprehensive regulatory scheme — the Controlled Substances Act — that governs interstate commerce. Without that comprehensive regulatory scheme as an anchor and a clear tie connecting the ban on possession to the regulation of the market in illicit drugs, the ban on marijuana possession would exceed Congress' commerce-clause power.

Of course, such an argument cuts in favor of, not against, the individual mandate in the healthcare reform law. The Affordable Care Act is a comprehensive regulatory scheme governing interstate commerce and the individual mandate plays an important role in furthering that regulatory framework.

In other words, upholding the mandate in the Affordable Care Act does not mean upholding any and every random, hypothetical mandate a crazy Congress might enact, assuming such a rogue Congress could survive in office.

Or consider another example. No one doubts that the government can often regulate ongoing economic activity — the sale and purchase of goods and services. Once we enter commerce as producers, sellers or buyers, the government can regulate our economic transactions and activities. No one denies this.

Again, think about the slippery slopes created by this acknowledged power. Go back to buying broccoli, the example of choice during the oral arguments. Congress might try to prohibit grocery stores from

selling any vegetable — or any food — other than broccoli. Or it might require people to purchase broccoli as a condition of purchasing other food. Want a hamburger? Gotta buy some healthy broccoli too. What if Congress required car dealers to sell a trunkful of broccoli with every new vehicle? Can Congress pull us down this cliff? If so, then who cares whether Congress can compel specific purchases directly? It can effectively compel people to buy designated goods by regu-